Laboratory Studies of the Sensitivity of Tropospheric Ozone to the Chemistry of Sea Salt Aerosol. Final Report, September 15, 1993--September 14, 1994 Page: 4 of 18
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3
I. OVERALL GOALS OF THIS PROJECT
Ozone plays a critical role in both the chemistry and radiation
balance of the troposphere. Not only does ozone react directly with
unsaturated organics, but it also photolyzes at wavelengths below 320
nm to form electronically excited O(1D) atoms; these react, in part,
with water to generate hydroxyl radicals (OH), the "universal
atmospheric oxidant" believed to drive the chemistry of both remote
and polluted atmospheres (Finlayson-Pitts & Pitts, 1986). Since
ozone is a greenhouse gas and absorbs in the 300 nm region, it also
impacts tropospheric radiation both in the infrared and the UV
(Demerjian et al, 1980; Ramanathan, 1988). As a result, understanding
the factors controlling tropospheric ozone levels is critical to our
understanding of a variety of issues in global chemistry and climate
change.
Chlorine atoms have the potential to contribute significantly to
the ozone balance in the free troposphere. They can react directly
with ozone,
Cl + 03 ---> C10 + 02 (1)
or alternatively, with organics:
Cl + RH ---> HCl + R (2)
The rate constant for reaction (2) is essentially diffusion-
controlled, even for relatively small alkanes. The alkyl radical
produced in (2) adds 02 to form alkylperoxy radicals (R02) which, in
the presence of sufficient NO, generate NO2. Photolysis of NO2 to
produce ground state O(3P) atoms, which add to 02, is the only known
source of anthropogenic ozone. Hence chlorine atom-organic reactions
may actually lead to the formation of ozone in the presence of
sufficient NO.
Reactions of alkali halides in sea salt particles are a
potential source of atomic chlorine, as well as to a lesser extent,
bromine. In addition, salt particles have been generated in the
troposphere in unusual situations such as the oil well burning in
Kuwait (e.g. see Lowenthal et al, 1993), and in the stratosphere by
the eruption of alkaline volcanoes such as El Chichon (Woods et al.,
1985). Hence the reactions of these alkali halides, especially those
producing precursors to atomic chlorine, are of great interest.
However, relatively little is known about the kinetics of these
gas-solid "heterogeneous" reactions. In addition, the atmospheric
fates of the gaseous halogen containing products of the salt
reactions are not well known. Surprisingly, there is significant
uncertainty in the absolute rate constants for the reactions of
chlorine atoms even with the simple alkanes, and no data are
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Finlayson-Pitts, B. J. Laboratory Studies of the Sensitivity of Tropospheric Ozone to the Chemistry of Sea Salt Aerosol. Final Report, September 15, 1993--September 14, 1994, report, November 15, 1994; Fullerton, California. (https://digital.library.unt.edu/ark:/67531/metadc1276317/m1/4/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.